As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand for batteries has also sharply increased as an energy source for the mobile devices. Also, much research on batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand of prismatic secondary batteries or pouch-type secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having high energy density, high discharge voltage, and high output stability, is very high.
Generally, a pouch-type secondary battery is constructed in a structure in which an electrode assembly is mounted in a pouch-type case made of an aluminum laminate sheet. Specifically, the pouch-type secondary battery is manufactured by forming a receiving part for receiving the electrode assembly in the laminate sheet and thermally welding an additional sheet separated from the laminate sheet or a sheet extending from the laminate sheet to the laminate sheet while the electrode assembly is received in the receiving part.
The receiving part may be formed in the pouch-type case by partially compressing the aluminum laminate sheet that has a thickness of approximately 113□ using a die and punch according to a process similar to a deep-throwing process. Since the thickness of the aluminum laminate sheet is small, however, the aluminum laminate sheet may break during the compression of the aluminum laminate sheet. For this reason, it is difficult to form the receiving part such that the receiving part has a depth of 15 mm or more.
Meanwhile, a separation-type battery case is constructed by overlapping two sheet-type cases in a sealing fashion. Consequently, it is required for both receiving parts to be overlapped with each other in position at while an electrode assembly is received in the receiving parts during the manufacture of a battery. When the electrode assembly is not received in the receiving parts in position, internal short circuits occur. For this reason, additional guide units are needed, which increases the manufacturing costs of the battery. In addition, the two sheet-type cases are coupled with each other at four sides thereof to form sealing parts. As a result, the two-unit battery case is in contact with the atmosphere at all the four sides thereof, and therefore, when the two-unit battery case is used for a long period of time, a possibility of the introduction of air into the two-unit battery case greatly increases, which reduces the service life of the battery.
In order to solve the above-mentioned problems, there have been proposed several technologies for forming two corresponding receiving parts at a one-unit sheet-type case and overlapping the two corresponding receiving parts with each other. For example, Japanese Patent Application Publication No. 2005-285503 and No. 2005-285506 disclose a technology for forming two corresponding receiving parts in a one-unit laminate sheet such that the two corresponding receiving parts are spaced a predetermined distance from each other and bending the middle region of the one-unit laminate sheet between the receiving parts while an electrode assembly is received in one of the receiving parts, thereby manufacturing a battery. This battery manufacturing technology reduces the depth of the receiving parts formed at the laminate sheet by approximately a half. Furthermore, a sealing part formed at one of four sides of the battery is maintained in a sealed state.
While the laminate sheet is compressed to form the two adjacent receiving parts in the laminate sheet, however, the middle region of the laminate sheet, which will be bent later, is stretched such that the two receiving parts can be formed at opposite sides of the middle region of the laminate sheet. As a result, the mechanical strength of the laminate sheet decreases as compared to when the laminate sheet is stretched in one direction with the result that the laminate sheet may easily break during forming the receiving parts and/or bending the laminate sheet.
Consequently, there is required a technology for preventing a one-unit battery case from breakage during forming electrode assembly receiving parts in the battery case and/or bending the battery case to overlap the receiving parts, thereby minimizing the product defect rate, and manufacturing a pouch-type battery through a simple assembly process.